Method of inspecting mask, mask inspection device, and method of manufacturing mask

ABSTRACT

There is provided a method of high-sensitively detecting both of a phase defect existing in a mask blank and a phase defect remaining after manufacturing an EUVL mask. When the mask blank is inspected, EUV light having illumination NA to be within an inner NA but a larger value is irradiated. When the EUVL mask is inspected, by using a dark-field imaging optical system including a center shielding portion for shielding EUV light and a linear shielding portion for shielding the EUV light whose width is smaller than a diameter of the center shielding portion, the center shielding portion and the linear shielding portion being included in a pupil plane, the EUV light having illumination NA as large as or smaller than the width of the linear shielding portion is irradiated.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent ApplicationNo. 2011-156288 filed on Jul. 15, 2011, the content of which is herebyincorporated by reference into this application.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a technique of manufacturing alithography mask used for forming a circuit pattern of a semiconductordevice. More particularly, the present invention relates to a techniqueeffectively applied to a method of inspecting a mask for extremeultra-violet ray exposure, a mask inspection device, and a method ofmanufacturing the mask, the mask being used for a lithography processusing so-called extreme ultra-violet ray (EUV light) exposure whosewavelength is about 10 to 15 nm.

BACKGROUND OF THE INVENTION

A semiconductor device (semiconductor integrated circuit device) isproduced by repeatedly using photolithography in which exposure light isirradiated onto a mask of an original plate, on which a circuit patternis drawn, so as to transfer the circuit pattern on a main plane of asemiconductor substrate (hereinafter, referred to as wafer) through areduced projection optical system.

However, in recent years, in response to demand for microfabrication ofthe semiconductor device, development of EUV lithography (hereinafter,referred to as EUVL) using EUV light whose wavelength is shorter thanthat of the light used for the exposure of the photolithography has beenadvanced. By using this EUVL, resolution can be improved, and afurther-microfabricated circuit pattern can be transferred.

In a wavelength range of the EUV light (whose center wavelength is, forexample, 13.5 nm), a transparency mask cannot be used because of lightabsorption of its material. Therefore, a multi-layered reflectionsubstrate which utilizes reflection by a multi-layered film made ofmolybdenum (Mo), silicon (Si), and others, is used as an EUVL mask blank(hereinafter, referred to as mask blank). An EUVL mask is configured byforming an absorber pattern on a plane of this mask blank (see in, forexample, “Introduction to Photomask Technology”, Kogyo ChousakaiPublishing Co., Ltd., written by Isao TANABE, Yohichi TAKEHANA, andMorihisa HOUGA, published on December 2006, pp. 266 to 268 (Non-PatentDocument 1)).

Also, since a transparent lens cannot be used, reflection-type exposureoptical system (reflection-type imaging optical system, EUV opticalsystem) made of only a reflection plane of a multi-layered film obtainedby alternately stacking Molybdenum (Mo) and silicon (Si) is used for thereduced projection optical system as described in, for example, JapanesePatent Application Laid-Open Publication No. 2007-158828 (PatentDocument 1). The light from a light source is homogenized through areflection-type illumination optical system, and is irradiated to theEUVL mask. The light irradiated to the EUVL mask reflects on the EUVLmask, and reaches the wafer through a reflection-type projection opticalsystem, so that the absorber pattern of the EUVL mask is projected onthe main plane of the wafer.

In the EUVL, even when slight height abnormality of about several nmoccurs in the plane of the mask blank, the height abnormality results inlarge change in phase of the EUV reflection light, and results indefects such as dimensional change or failure of resolution in thetransfer of the absorber pattern onto the main plane of the wafer. Sucha defect which results in the phase change is called phase defect.Accordingly, it is required to detect the phase defect at a stage of amask blank obtained prior to coating of the absorber pattern.

As a general method of inspecting the mask blank, there are a method ofdetecting a foreign material and a method of detecting a bright-fieldimage (microscope image) from diffused reflection light caused byirradiating laser light to the mask blank. However, the influence of thephase defect also depends on an internal structure of the multi-layeredfilm, and therefore, it is considered that an inspection method atwavelength (the same wavelength) of detecting the defect with usingdetection light whose wavelength is the same as that of the EUV lightused for the exposure is suitable. As one example of this method, forexample, Japanese Patent Application Laid-Open Publication No.2003-114200 (Patent Document 2) discloses a method with using adark-field image inspection image. Also, for example, Japanese PatentApplication Laid-Open Publication No. 2007-219130 (Patent Document 3)discloses an inspection method of differentiating concavity andconvexity of a plane of the phase defect. Further, for example, JapanesePatent Application Laid-Open Publication (Translation of PCTApplication) No. 2002-532738 (Patent Document 4) discloses a techniqueof improving a projection image in pattern transfer by an exposuredevice by adjusting a contour of the absorber pattern if the absorberpattern is formed in a state that the phase defect already exists.

SUMMARY OF THE INVENTION

In the dark-field inspection method with using the EUV light in theabove-described Patent Document 2, the phase defect of the mask blankcan be high-sensitively detected as a bright point. Further, thedocument discloses that a shielding portion having a predetermined shapeis additionally provided to an inspection optical system when an EUVLmask having an absorber pattern is inspected in order to avoid influenceof a diffracted-light component which is a cause of increasing abackground level of an inspection signal. However, the additionalprovision of the shielding portion causes a risk that a transparentamount of scattered light caused by the phase defect is reduced, whichresults in reduction of detection sensitivity for the phase defect.

Also, in the inspection method in the above-described Patent Document 3,presence/absence of defects in the plane of the mask blank and thedifferentiation of the concavity and convexity therein can be judged.However, there is no consideration of the influence of the diffractedlight caused when the EUVL mask having the absorber pattern isinspected.

Meanwhile, the inspection method in the above-described Patent Document4 discloses a method by which the EUVL mask can be handled as anon-defective product even when the phase defect remains after formingthe absorber pattern. However, the document does not describe a methodof inspecting the phase defect remaining after forming the absorberpattern.

As described above, even in any inspection method described above, it isdifficult to high-sensitively detect both of the phase defect remainingin the mask blank and the phase defect substantially remaining aftermanufacturing the EUVL mask.

Also, when the phase defect of the multi-layered film which is difficultto be adjusted is detected, a process does not proceed to a step offorming the absorber pattern even if the defect is a micro-size defect,and the mask blank is handled as a defective product and is discarded.According to consideration of the present inventors, if the phase defectis at a position covered by the formed absorber pattern, the mask blankis available. However, depending on a total number of the detected phasedefects, it is difficult to cover all the phase defects, and therefore,it is required to specify a defect not covered thereby and remaining inthe EUVL mask. Eventually, although it is required to detect the phasedefect so as to avoid the influence of the diffracted light of theabsorber pattern, it is difficult to high-sensitively perform thedetection as described above.

A preferred aim of the present invention is to provide a method ofhigh-sensitively detecting both of a phase defect remaining in a maskblank and a phase defect remaining after manufacturing an EUVL mask.

Also, another preferred aim of the present invention is to provide adefect inspection device of high-sensitively detecting both of a phasedefect remaining in a mask blank and a phase defect remaining aftermanufacturing an EUVL mask.

Further, still another preferred aim of the present invention is toprovide a method of manufacturing an EUVL mask capable of removing acritical phase defect remaining in the EUVL mask by detecting those of amask blank and the EUVL mask by the same defect inspection device.

The above and other preferred aims and novel characteristics of thepresent invention will be apparent from the description of the presentspecification and the accompanying drawings.

The typical embodiments of the inventions disclosed in the presentapplication will be briefly described as follows.

This embodiment is a method of inspecting an EUVL mask, and the methodincludes: a step of irradiating EUV light to a mask; a step of imagingthe EUV light which reflects from the mask onto a light-receiving planeof an image detector through a dark-field imaging optical system; and astep of detecting a detection signal of a phase defect existing in themask from detection signals obtained by the image detector. When the EUVlight is irradiated to the mask, illumination NA (numerical aperture) ofthe EUV light is changed depending on a case that the absorber patternexists in the mask and a case that the absorber pattern does not existin the mask.

Also, this embodiment is an inspection device for an EUVL mask, and theinspection device includes: a stage movable in X and Y directions onwhich the EUVL mask is loaded; a light source of generating EUV light;an illumination optical system of irradiating the EUV light to the EUVLmask; illumination aperture of changing illumination NA (numericalaperture) when the EUV light is irradiated to the EUVL mask; adark-field imaging optical system of collecting scattered light causedfrom the mask to form a dark-field inspection image; an image detectorof acquiring the dark-field inspection image as a pixel signal; and anaperture driving unit of adjusting the illumination aperture based oninformation of an absorber pattern.

Further, this embodiment is a method of manufacturing an EUVL mask, andthe method includes: (a) a step of preparing a mask blank, on which amulti-layered film for reflecting EUV light is formed, on a main planeof a substrate; (b) a step of irradiating the EUV light to the maskblank to detect a phase defect of the mask blank; (c) a step ofmemorizing a positional coordinate of the phase defect detected in thestep of (b) and of providing a priority order, which indicates a degreeof influence on pattern transfer, to the phase defect; (d) a step offorming an absorber pattern on the multi-layered film of the mask blankas covering the phase defect of the mask blank in descending order ofthe priority for forming the mask; and (e) a step of detecting the phasedefect of the mask by an inspection device with using the EUV light asan inspection light.

The effects obtained by typical embodiments of the present inventiondisclosed in the present application will be briefly described below.

A method of high-sensitively detecting both of a phase defect remainingin a mask blank and a phase defect remaining after manufacturing an EUVLmask can be provided.

Also, a defect inspection device of high-sensitively detecting both ofthe phase defect remaining in the mask blank and the phase defectremaining after manufacturing the EUVL mask can be provided.

Further, a method of manufacturing the EUVL mask capable of removing acritical phase defect remaining in the EUVL mask by detecting those ofthe mask blank and the EUVL mask by the same defect inspection devicecan be provided.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1A is a plan view of a principal part of a plane on which anabsorber pattern of an EUVL mask is formed, according to a firstembodiment of the present invention;

FIG. 1B is a cross-sectional view of a principal part illustrating anenlarged part along line A-A of FIG. 1A;

FIG. 2 is a schematic diagram of an EUV projection exposure deviceaccording to the first embodiment of the present invention;

FIG. 3A is a cross-sectional view of a principal part of a mask blankhaving a phase defect, according to the first embodiment of the presentinvention;

FIG. 3B is a cross-sectional view of a principal part of an EUVL maskobtained by forming an absorber pattern and a buffer layer on the maskblank having the phase defect, according to the first embodiment of thepresent invention;

FIG. 4 is a schematic diagram illustrating an entire structure of a maskinspection device of collecting a dark-field inspection image of themask blank or the EUVL mask with using EUV light, according to the firstembodiment of the present invention;

FIG. 5A is a diagram explaining a relationship between a dark-fieldinspection image obtained when the phase defect remains in the maskblank and scattered light passing through a pupil plane of aSchwarzschild optical system according to the first embodiment of thepresent invention, and is an enlarged diagram of a part including adark-field imaging optical system and the mask blank;

FIG. 5B is a diagram explaining a relationship between a dark-fieldinspection image obtained when the phase defect remains in the maskblank and scattered light passing through a pupil plane of aSchwarzschild optical system according to the first embodiment of thepresent invention, and is a schematic diagram illustrating a pupil planeof a dark-field imaging optical system;

FIG. 5C is a diagram explaining a relationship between a dark-fieldinspection image obtained when the phase defect remains in the maskblank and scattered light passing through a pupil plane of aSchwarzschild optical system according to the first embodiment of thepresent invention, and is a schematic diagram illustrating a pupil planeof a dark-field imaging optical system including linear shieldingportions;

FIG. 6A is a diagram explaining a result obtained by observing the phasedefect remaining in the mask blank with using the dark-field imagingoptical system according to the first embodiment of the presentinvention, and is a diagram illustrating light-intensity distribution ofa dark-field inspection image in a region where the phase defect exists;

FIG. 6B is a diagram explaining a result obtained by observing the phasedefect remaining in the mask blank with using the dark-field imagingoptical system according to the first embodiment of the presentinvention, and is a diagram explaining a relationship between pixel anda dark-field inspection image of a phase defect which is imaged on alight-receiving plane of a two-dimensional array sensor;

FIG. 7A is a diagram explaining a result obtained by observing a phasedefect existing between absorber patterns adjacent to each other inobservation of the EUVL mask having the absorber pattern according tothe first embodiment of the present invention, and is an enlargeddiagram of a part including the dark-field imaging optical system andthe mask blank (diagram explaining a relationship between the dark-fieldimaging optical system and the EUV light diffracted from the absorberpattern);

FIG. 7B is a diagram explaining a result obtained by observing a phasedefect existing between absorber patterns adjacent to each other inobservation of the EUVL mask having the absorber pattern according tothe first embodiment of the present invention, and is a diagramillustrating light-intensity distribution of a dark-field inspectionimage in the region where the phase defect exists in a case withcontaining the phase defect and the absorber pattern;

FIG. 7C is a diagram explaining a result obtained by observing a phasedefect existing between absorber patterns adjacent to each other inobservation of the EUVL mask having the absorber pattern according tothe first embodiment of the present invention, and is a diagramillustrating light-intensity distribution of the dark-field inspectionimage in a case with containing only the absorber pattern;

FIG. 8A is a diagram explaining a result obtained by observing the phasedefect existing between absorber patterns adjacent to each other inobservation of the EUVL mask having the absorber pattern according tothe first embodiment of the present invention, and is a diagramexplaining a relationship between a pupil plane of the dark-fieldimaging optical system and diffracted light components from an edge ofthe absorber pattern;

FIG. 8B is a diagram explaining a result obtained by observing the phasedefect existing between absorber patterns adjacent to each other inobservation of the EUVL mask having the absorber pattern according tothe first embodiment of the present invention, and is a diagramillustrating distribution of detection signal intensity obtained as apixel signal column;

FIG. 9 is a process chart explaining a flow of a mask defect inspectionaccording to the first embodiment of the present invention;

FIG. 10 is a diagram illustrating one example of a phase defect on amask blank which is detected with using a method of inspecting a maskblank according to a second embodiment of the present invention;

FIG. 11A is a plan diagram of a principal part of a mask illustrating anexample that the phase defect is completely covered by the absorberpattern, according to the second embodiment of the present invention;

FIG. 11B is a plan diagram of a principal part of a mask illustrating anexample that the phase defect is not covered by the absorber pattern,according to the second embodiment of the present invention; and

FIG. 12 is a process chart explaining a flow of a method ofmanufacturing the mask according to the second embodiment of the presentinvention.

DESCRIPTIONS OF THE PREFERRED EMBODIMENTS

In the embodiments described below, the invention will be described in aplurality of sections or embodiments when required as a matter ofconvenience. However, these sections or embodiments are not irrelevantto each other unless otherwise stated, and the one relates to the entireor a part of the other as a modification example, details, or asupplementary explanation thereof.

Also, in the embodiments described below, when referring to the numberof elements (including number of pieces, values, amount, range, and thelike), the number of the elements is not limited to a specific numberunless otherwise stated or except the case where the number isapparently limited to a specific number in principle. The number largeror smaller than the specific number is also applicable. Further, in theembodiments described below, it goes without saying that the components(including element steps) are not always indispensable unless otherwisestated or except the case where the components are apparentlyindispensable in principle. Similarly, in the embodiments describedbelow, when the shape of the components, positional relation thereof,and the like are mentioned, the substantially approximate and similarshapes and the like are included therein unless otherwise stated orexcept the case where it is conceivable that they are apparentlyexcluded in principle. The same goes for the numerical value and therange described above.

Also, in some drawings used in the following embodiments, hatching isused even in a plan view so as to make the drawings easy to see.Further, in the following embodiments, the term “wafer” mainly indicatesa silicon (Si) monocrystalline wafer and it indicates not only the samebut also a silicon-on-insulator (SOI) wafer, an insulating filmsubstrate for forming an integrated circuit thereon, or the like. Theshape of the wafer includes not only a circular shape or a substantiallycircular shape but also a square shape, a rectangular shape, and thelike.

Also, components having the same function are denoted by the samereference symbols throughout the drawings for describing theembodiments, and the repetitive description thereof is omitted.Hereinafter, the embodiments of the present invention will be explainedin detail based on the drawings.

First Embodiment

In order to clarify a purpose of a method of inspecting an EUVL maskaccording to a first embodiment, first, a structure of the EUVL mask anda structure of a projection optical system (a reduced projection opticalsystem, a reflection-type exposure optical system, a reflection-typeimaging optical system, and an EUV optical system) equipped in an EUVLexposure device will be explained with reference to FIGS. 1A, 1B, and 2.FIG. 1A is a plan view of a principal part of a plane on which anabsorber pattern of the EUVL mask is formed, and FIG. 1B is across-sectional view of a principal part illustrating an enlarged partalong line A-A of FIG. 1A. Also, FIG. 2 is a schematic diagram of theEUV projection exposure device.

As illustrated in FIG. 1A, a device pattern area “MDE” having a circuitpattern of a semiconductor integrated circuit device is provided in acenter portion of an EUVL mask “M”, and alignment mark areas “MA1”,“MA2”, “MA3”, and “MA4” including a mark for positioning the EUVL maskM, a wafer alignment mark, and others are arranged in a peripheralportion thereof.

Also, as illustrated in FIG. 1B, a mask blank of the EUVL mask Mincludes: a substrate “MS” made of quartz glass or low thermal expansionglass; a multi-layered film “ML” obtained by alternately stackingmolybdenum (Mo) and silicon (Si) (for example, about 40 layers arestacked for each of them) which are formed on a main plane of thesubstrate MS; a capping layer “CAP” formed on the multi-layered film ML;and a metal film “CF” for electrostatic chuck of the EUVL mask M formedon a rear plane of the substrate MS (a plane opposite to the mainplane). A thickness of the substrate MS is, for example, about 7 to 8mm, and a thickness of the multi-layered film ML is, for example, about300 nm. Further, on the capping layer CAP, an absorber pattern “ABS” isformed via a buffer layer “BUF”. A thickness of the absorber pattern ABSis, for example, about 50 to 70 nm.

Next, the EUV projection exposure device using the EUVL mask will beexplained with reference to FIG. 2 illustrating its concept.

As illustrated in FIG. 2, the EUV light whose center wavelength is 13.5nm and which is emitted from a light source 1 is irradiated through anillumination optical system 2 formed of a mirror reflector made of amulti-layered film to a plane (hereinafter, referred to as patternplane) on which the absorber pattern of the EUVL mask is formed. Thereflected light from the pattern plane passes through a reducedprojection optical system 3 formed of a mirror reflector made of amulti-layered film, so that the pattern is transferred on a main planeof a wafer 4. Since the wafer is loaded on a stage 5, a lot of thepatterns are transferred on a desirable region of the wafer 4 byrepeating movement of the stage 5 and the pattern transfer.

Next, the phase defect caused in the mask blank of the EUVL mask will beexplained with reference to FIGS. 3A and 3B. FIG. 3A is across-sectional view of a principal part of a mask blank having a phasedefect, and FIG. 3B is a cross-sectional view of a principal part of theEUVL mask obtained by forming the absorber pattern and the buffer layeron the mask blank having the phase defect.

The cross-sectional view of the principal part of the mask blankillustrated in FIG. 3A illustrates one example that a concave-shapedphase defect “PD” is caused as a result of coating the above-describedmulti-layered film ML in a state that a micro void still exists in themain plane of the substrate MS when the multi-layered film ML is coatedon the substrate MS.

If the buffer layer BUF and the absorber pattern ABS are formed in thestate that this phase defect remains, the concave-shaped phase defect PDremains between the absorber patterns ABS adjacent to each other asillustrated in FIG. 3B. By the existence of the void of the phase defectPD of about 2 to 3 nm, a pattern projection image transferred on themain plane of the wafer in the EUVL is disturbed, a defect is caused inthe transferred pattern on the main plane of the wafer. While FIGS. 3Aand 3B illustrate one example of the void defect, a micro swell defectalso causes the similar phase defect.

In a conventional photolithography mask, even if concavity/convexity ofabout several nm exists in a plane of a transparent mask blank, theconcavity/convexity is ignorable. Therefore, there is asubstantially-large difference in the defect transfer between the EUVLmask and the conventional photolithography mask. Therefore, in the EUVLmask, it is required to avoid the causing of the phase defect PD of themask blank, which results in phase difference. Therefore, in the EUVLmask, it is required to detect the phase defect PD of the mask blank ata stage of the mask blank obtained prior to the formation of theabsorber pattern ABS and the buffer layer BUF.

Next, an entire structure of a mask inspection device according to thefirst embodiment will be explained with reference to FIG. 4. FIG. 4 is aschematic diagram illustrating the entire structure of the maskinspection device of collecting the dark-field inspection image of themask blank or the EUVL mask with using EUV light. While the entirestructure will be explained here with citing a mask inspection deviceused for inspecting the mask blank as an example, a mask inspectiondevice with the similar structure is also used for the EUVL mask.

The mask inspection device includes: a light source (EUV light source,or plasma light source) 6 for generating EUV light (EUV inspectionlight, illumination light, or irradiation light) “BM”; a mask stage 7for loading the mask blank MB thereon; an illumination optical system“CIO”; an imaging optical system “DPO”; a two-dimensional array sensor(image detector) “SE”; a sensor circuit 8; a pattern memory 9; a signalprocessing circuit 10; a timing controlling circuit 11; a mask-stagecontrolling circuit 12; a system controlling computer 13 for controllingoperation of an entire device; and others. Also, it includes a data file14 for storing various data related to a mask pattern.

The light source 6 includes a wavelength-selective filter, means forpressure bulkhead, means for suppressing dispersion particles, or othersif required. The imaging optical system DPO includes a concave mirror“L1” and a convex mirror “L2”, and is a Schwarzshild optical systemconfiguring a dark-field imaging optical system having, for example, anouter NA (numerical aperture) of 0.2, an inner NA (which defines a lightshielding portion at the center of pupil plane) of 0.1, and 26-foldmagnification.

The mask blank MB for which the presence/absence of the phase defect isto be inspected is loaded on the mask stage 7 movable in three axisdirections of X, Y, and Z. The EUV light BM whose center wavelength is13.5 nm emitted from the light source 6 is converted through theillumination optical system CIO into convergent beam, and then, passesthrough an aperture unit “APT” for adjusting a beam size, is bent by amulti-layered mirror “PM”, and is irradiated to a predetermined regionof the mask blank MB. Here, the aperture unit APT plays a role ofillumination aperture for changing the illumination NA, and a size ofthe aperture unit APT, that is, a size of the illumination aperture iscontrolled by an aperture driving unit (not illustrated) for adjustingthe illumination aperture. A position of the mask blank MB is obtainedas positional information of the mask stage 7 by reading a position ofthe mirror 15, which is fixed at the mask stage 7, with using a laserlength-measuring machine 16. This positional information is transmittedto a position circuit 17, so that it can be recognized by the systemcontrolling computer 13. Meanwhile, a part of the EUV light BM isbranched by a beam splitter “BSP” to monitor light quantity by anEUV-light sensor 18, so that a threshold value for a signal processingcan be set in an illumination intensity correcting circuit 19. This beamsplitter BSP can be formed by a multi-layered film obtained byalternately stacking, for example, about several to ten pairs ofmolybdenum (Mo) and silicon (Si). The means for branching the part ofthe EUV light BM and guiding it to the EUV-light sensor 18 is notlimited as the beam splitter BSP. For example, a multi-layered filmmirror for reflecting only EUV light which is a part of a peripheralportion of light flux of the EUV light BM in a predetermined directionmay be arranged, and the EUV light of the part may be guided to theEUV-light sensor 18.

The light scattered by the phase defect among the reflection light fromthe mask blank MB passes through the imaging optical system DPO to formconvergent beam “SLI”, and is collected to the two-dimensional arraysensor (image detector) SE. That is, a dark-field inspection image ofthe mask blank MB is formed in the two-dimensional array sensor SE, and,as a result, the phase defect PD remaining in the mask blank MB isdetected as a bright point in the inspection image. Information of aposition of the detected phase defect PD, magnitude of a defect signalthereof, and others is memorized in a memory device 20, and besides,various types of information can be observed via a pattern monitor 21 oran image outputting unit 22.

Next, the method of inspecting the mask according to the firstembodiment will be explained in detail.

<<Method of Inspecting Mask Blank>>

First, a relationship between the dark-field inspection image in thecase that the phase defect exists in the mask blank and the scatteredlight passing through a pupil plane of the Schwarzschild optical systemwill be explained with reference to FIGS. 5A, 5B, and 5C.

FIG. 5A is an enlarged diagram of a part including the imaging opticalsystem DPO and the mask blank MB illustrated in FIG. 4 described above.The EUV light BM is bent by the multi-layered film mirror PM, and isirradiated to a predetermined region of the mask blank MB. Among thelight 30 reflected and scattered from the phase defect PD on the planeof the mask blank MB, the light proceeding toward a direction “31-1” ofan annular region defined as a region inside the concave mirror L1 andoutside the convex mirror L2 reflects on the concave mirror L1 toproceed in an inner direction indicated by a direction “31-2”, andfurther reflects on the convex mirror L2 to proceed in one directionindicated by a direction “31-3”, and proceed toward the two-dimensionalarray sensor SE.

FIG. 5B is a schematic diagram illustrating the pupil plane of theimaging optical system DPO according to the first embodiment. Theannular region defined as the region from the inside of the concavemirror Li to the outside of the convex mirror L2 described in FIG. 5Aabove corresponds to a region between the outer NA (whose symbol is“NAOU”) and the inner NA (whose symbol is “NAIN”). The inner NA (whosesymbol is NAIN) corresponds to a region shielded by the convex mirrorL2, and the convex mirror L2 is held by beams 32-1, 32-2, and 32-3.These beams 32-1, 32-2, and 32-3 are light-shielding substances againstthe scattered light passing through the imaging optical system DPO, andtherefore, their shapes are thin, and they are provided at positionsshifted from an X-direction axis (X axis) and a Y-direction axis (Yaxis) so as not to shield the scattered light in only a specificdirection. A symbol “NAILL” in the same drawing indicates theillumination NA obtained when the EUV light BM is irradiated to the EUVLmask.

FIG. 5C is a schematic diagram illustrating a pupil plane of an imagingoptical system DPO including linear shielding portions according to thefirst embodiment. As illustrated in FIG. 5C, linear shielding portions33-1, 33-2, 33-3, and 33-4 are provided along each of the X axis and theY axis in the pupil plane of the imaging optical system DPO, and theirwidths W are set to be a smaller value than a diameter of the inner NA(whose symbol is NAIN). These linear shielding portions 33-1, 33-2,33-3, and 33-4 may have a form allowed to be inserted or attached, or aform also including the beam structure for supporting the convex mirrorL2.

A result obtained by observing the phase defect existing in the maskblank with using the dark-field imaging optical system having the pupilplane illustrated in FIG. 5B or the dark-field imaging optical systemhaving the pupil plane illustrated in FIG. 5C will be explained withreference to FIGS. 6A and 6B. FIG. 6A is a diagram illustratinglight-intensity distribution of a dark-field inspection image in aregion where the phase defect exists, and FIG. 6B is a diagramexplaining a relationship between pixel and the dark-field inspectionimage of the phase defect which is imaged on a light-receiving plane ofthe two-dimensional array sensor.

When the phase defect (corresponding to, for example, the phase defectPD illustrated in the above-described FIG. 3A) existing in the maskblank MB is observed with using the imaging optical system DPO explainedwith reference to the above-described FIGS. 5A to 5C, light-intensitydistribution 34 of the dark-field inspection image as illustrated inFIG. 6A is obtained. Practically, signals obtained in thetwo-dimensional array sensor SE are obtained as not such alight-intensity distribution of the dark-field inspection image but aseries of pixel light intensity stored for each pixel.

Here, when the mask blank MB is observed, the EUV light is irradiated tothe mask blank MB, the EUV light having the illumination NA whose lightflux is within the inner NA (whose symbol is NAIN) but larger than thewidths W of the linear shielding portions in the pupil plane of theimaging optical system DPO illustrated in the above-described FIG. 5B or5C, so that a contrast of the dark-field inspection image obtained asthe pixel signal is improved.

FIG. 6B is a diagram explaining a relationship between the pixel and thedark-field inspection image with an enlarged image (light-intensitydistribution 34) of the phase defect which has been magnified 26 timesto be imaged on the light-receiving plane of the two-dimensional arraysensor SE. In the drawing, a symbol “Pxy” indicates a size of one sideof the pixel, a symbol 35 indicates a boundary between the pixels, asymbol 36 indicates a pixel with the enlarged image of the phase defect,and a symbol 37 indicates a pixel without the enlarged image of thephase defect. The light quantity stored in the pixel 36 with theenlarged image (light-intensity distribution 34) of the phase defect ismore than the light quantity stored in the pixel 37 without the enlargedimage of the phase defect, and therefore, a position of the pixel withthe phase defect can be specified.

<<Method of Inspecting EUVL Mask>>

Next, in observation of the EUVL mask M having the absorber pattern, aresult obtained by observing a phase defect (corresponding to, forexample, the phase defect PD illustrated in FIG. 3B described above)existing between the absorber patterns adjacent to each other will beexplained with reference to FIGS. 7A, 7B, 7C, 8A, and 8B. FIG. 7A is anenlarged diagram of a part including the imaging optical system DPO andthe EUVL mask M illustrated in the above-described FIG. 4 (diagramexplaining a relationship between the dark-field imaging optical systemand the EUV light diffracted from the absorber pattern), FIG. 7B is adiagram illustrating light-intensity distribution of the dark-fieldinspection image in the region where the phase defect exists in the casewith the phase defect and the absorber pattern, and FIG. 7C is a diagramillustrating light-intensity distribution of the dark-field inspectionimage in the case with only the absorber pattern. Also, FIG. 8A is adiagram explaining a relationship between the pupil plane of the imagingoptical system DPO and diffracted-light components from an edge of theabsorber pattern, and FIG. 8B is a diagram illustrating intensitydistribution of a detection signal obtained as a pixel signal column.

As illustrated in FIG. 7A, as the light reflected from the pattern planeof the EUVL mask M, high-order diffracted-light components 38 and 39caused depending on periodicity of the absorber pattern in addition tothe scattered light caused by the phase defect are captured by theconcave mirror L1 to form the dark-field inspection image on thelight-receiving plane of the two-dimensional array sensor SE. As aresult, as illustrated in FIG. 7B, light-intensity distribution 40 ofthe dark-field inspection image of the phase defect and diffracted-lightintensity distribution 41 from the edge of the absorber pattern areobtained. FIG. 7C illustrates the light-intensity distribution of thedark-field inspection image obtained in a case that only thediffracted-light components from the edge of the absorber pattern areobtained without the dark-field inspection image of the phase defect.

Here, when the EUVL mask M is observed, the EUV light is irradiated tothe EUVL mask M, the EUV light having the illumination NA whose lightflux is as large as or smaller than the thicknesses (widths) of thelinear shielding portions provided along each of the X axis and the Yaxis in the pupil plane of the imaging optical system DPO illustrated inthe above-described FIG. 5C.

FIG. 8A is a diagram explaining a relationship between the pupil planeof the imaging optical system DPO and diffracted-light components fromthe edge of the absorber pattern. A circular region 43-1 indicates asize of the illumination NA and a region size to which a zero-orderreflection component reaches from the pattern plane of the EUVL mask M,and is shielded by the center shielding portion. Further, the linearshielding portions shield most of a first-order diffracted-lightcomponent 43-2, a second-order diffracted-light component 43-3, athird-order diffracted-light component 43-4, a fourth-orderdiffracted-light component 43-5, a minus first-order diffracted-lightcomponent 43-6, a minus second-order diffracted-light component 43-7, aminus third-order diffracted-light component 43-8, and a minusfourth-order diffracted-light component 43-9 from the edge of theabsorber pattern.

As a result, in a detection signal 45 obtained in the case with thelinear shielding portions as compared to a detection signal 44 obtainedin the case without the linear shielding portion as illustrated in FIG.8B, while an intensity level of the signal is lowered, the signal isdetected as a pixel signal whose intensity of the pixel with the phasedefect is relatively brighter than that in the periphery thereof. Thatis, in the detection signal 45 obtained in the case with the linearshielding portions, the pixel signal without the phase defect has asufficient small value, and therefore, the contrast of the detectedimage is improved.

Each pattern of most of semiconductor devices has basically a patterngroup arranged in an X direction and a Y direction. Therefore, it issufficient to arrange the above-described linear shielding portionsalong both directions of the X and Y directions of the pupil plane ofthe imaging optical system DPO.

When the illumination NA is set as large as the inner NA similarly tothe case of the mask blank inspection, the high-order diffracted-lightcomponent cannot be shielded by the linear shielding portions, andpasses through the pupil plane of the imaging optical system DPO, and,as a result, the contrast of the dark-field inspection image obtained asthe pixel signal is lowered. However, by narrowing the illumination NA,the contrast of the dark-field inspection image can be improved, and thephase-defect detection with high sensitivity can be performed.

A flow of the mask defect detection according to the first embodimentdescribed above will be explained with reference to the above-describedinspection device illustrated in FIG. 4 and a flowchart illustrated inFIG. 9.

<Step S101>

First, the mask blank or the EUVL mask which is a sample to be inspectedis loaded on the stage 7 of the inspection device. The reference mark onthe EUVL mask is read if required to position the stage 7 by themask-stage controlling circuit 12. This position is read by a laserlength-measuring machine (laser interferometer) 16, and is memorized asa reference coordinate on the EUVL mask.

<Step S102>

The information of the sample to be inspected, that is, information ofdetermining the mask blank obtained prior to the formation of theabsorber pattern or the EUVL mask having the absorber pattern (mask withthe absorber pattern) is inputted. In the case of the EUVL mask, if itis known that a region to be inspected is limited, information of theinspection region is also inputted if required.

<Steps S103 to S104>

In the case that the sample to be inspected is the mask blank, theillumination aperture for defining the illumination NA of the EUV light,that is, the aperture APT is controlled by the aperture driving unit soas to set the illumination NA to be within the inner NA but a largervalue, and the light is irradiated to the mask blank.

<Step S105>

Then, the phase defect is detected over the whole plane of the maskblank, and the positional information and the signal intensityinformation of the detected phase defect are memorized. The positionalinformation of the phase defect can be calculated from positionalinformation of the pixel at which the signal with the phase defect isobtained.

<Step S106>

Further, a number is provided to the signal intensities in a descendingorder, and this is also memorized as the priority order indicating thedegree of the influence of the phase defect on the transfer pattern.

<Steps S103 to S107>

On the other hand, in the step of S103, in the case that the sample tobe inspected is the EUVL mask having the absorber pattern, the apertureAPT for defining the illumination NA of the EUV light is controlled toset the illumination NA so as to be a sufficiently smaller value thanthe inner NA and as large as (see FIG. 5C described above) or smallerthan the widths of the linear shielding portions, and the light isirradiated to the EUVL mask.

<Step S108>

Within the region to be inspected, which has been previously inputted,the phase defect of the EUVL mask is detected. Even if the phase defectexists at the stage of the mask blank, this does not substantiallybecome the defect as long as the phase defect is covered by the absorberpattern, and therefore, the detection signal of the phase defect is notobtained.

<Step S109>

The information of the remaining phase defect (which is the phase defectnot covered by the absorber pattern and substantially affecting thepattern transfer) is memorized. If the phase defect is covered by theabsorber pattern, the detection signal of the phase defect is notobtained at this moment. If it is not covered, it is detected as thephase defect remaining in the EUVL mask.

As described above, according to the first embodiment, the phase defectremaining in the reflection plane of the multi-layered film can bedetected at the high detection sensitivity in both of the mask blankobtained prior to the formation of the absorber pattern and the EUVLmask having the absorber pattern.

Second Embodiment

In a second embodiment, a method of manufacturing the EUVL maskincluding the step of inspecting the phase defect of the mask blank andthe step of inspecting the phase defect remaining in the EUVL maskexplained in the above-described first embodiment will be explained, andthe method is capable of apparently reducing or eliminating theinfluence of the phase defect by adjusting a shape of the absorberpattern in the periphery of the phase defect when it is determined thatthe remaining phase defect affects the transfer of the absorber pattern.

First, a mask blank MB is prepared. FIG. 10 is a diagram illustratingone example of the phase defect on the mask blank MB detected by thedefect inspection for the mask blank which has been explained in theabove-described first embodiment. The phase defects 46-1, 46-2, 46-3,and 46-4 are defects critically affecting when the absorber patternformed on the mask blank MB is transferred on the main plane of thewafer by the projection exposure device, and are phase defects to whichthe high priority order is provided. On the other hand, the phasedefects 47-1, 47-2, and 47-3 are phase defects to which the low priorityorder is provided. For all of these phase defects, their positions areobtained in a coordinate system defined by reference marks 48-1, 48-2,48-3, and 48-4 provided on the mask blank MB.

Next, the absorber pattern is formed on the mask blank MB to form theEUVL mask. Finally, the structure of the EUVL mask becomes the samestructure illustrated in FIG. 1 in the above-described first embodiment.At this time, in order to cover the above-described phase defects towhich the high priority-order numbers are provided by the absorberpattern as completely as possible, a position at which the absorberpattern is to be formed is determined with respect to the referencemarks 48-1, 48-2, 48-3, and 48-4 to form the absorber pattern.

One example of the defects is illustrated in FIGS. 11A and 11B. FIG. 11Ais a plan view of a principal part of a mask illustrating an examplethat both of phase defects 51-1 and 51-2 having the high priority orderare completely covered by the absorber pattern ABS. That is, the phasedefects disappear on the EUVL mask. On the other hand, FIG. 11B is aplan view of a principal part of a mask illustrating an example thatboth of the phase defects 51-1 and 51-2 are not covered by the absorberpattern ABS and remain in the EUVL mask. If the positioning failureoccurs in the formation of the absorber pattern, the defect having eventhe high priority order cannot be covered by the absorber pattern ABS insome cases.

By the inspection device using the EUV light as the inspection light, itis verified whether the phase defect is covered or not in the EUVL maskon which such an absorber pattern is formed. More particularly, theinspection method for the EUVL mask described in the first embodimentabove is effective. At this time, as the inspection region of the EUVLmask, even a narrow region including the position at which the phasedefect has been detected in the above-described inspection for the maskblank is sufficient to be inspected. Although the handling of theremaining phase defect is a problem, it is considered that, for example,the phase defect 52-1 has small influence because of sufficiently farfrom the absorber pattern. If the influence is large, the absorberpattern is locally formed for only the phase defect, so that theinfluence of the phase defect can be reduced.

Also, regarding the phase defect 52-2 remaining between the absorberpatterns adjacent to each other, the influence in the pattern transferby the exposure device can be reduced by the method disclosed in, forexample, Japanese Patent Application Laid-Open Publication No.2002-532738 (Translation of PCT Application) (Patent Document 4), thatis, by adjusting the contour of the absorber pattern adjacent to thephase defect.

If the influence of the phase defect cannot be reduced even by theformation of the absorber pattern or the adjustment of the contourdescribed above, the EUVL mask is a defective product. However, in mostcases, the critical phase defect is covered by the absorber pattern, andtherefore, the influence of the phase defect remaining in the EUVL maskcan be sufficiently reduced.

A flow of the method of manufacturing the mask according to the secondembodiment described above will be explained with reference to aflowchart illustrated in FIG. 12.

<Step S201>

First, a mask blank obtained by coating a multi-layered film and acapping layer on a substrate is prepared.

<Step S202>

The mask blank is inspected with using the inspection method which hasbeen explained in the above-described first embodiment.

<Steps S203 to S204>

In the case that the phase defect exists in the mask blank,simultaneously with the provision of the priority order to the detectedphase defect, the priority order and the positional coordinate (defectcoordinate) of the phase defect with respect to the predeterminedreference mark are memorized.

<Step S205>

The absorber pattern is formed on the mask blank. At this time, theposition of the absorber pattern is calculated so as to cover theabove-described phase defect having the high priority order by theabsorber pattern as completely as possible to form the pattern.

<Step S206>

The defect inspection for the absorber pattern is performed. If thephase defect exists in the absorber pattern, the portion to be adjustedand an adjustment degree are separately calculated.

<Step S207>

The EUVL mask having the absorber pattern is inspected with using theinspection method which has been explained in the above-described firstembodiment. In this inspection, the inspection over the whole plane ofthe EUVL mask is not always necessary, and the inspection may beperformed for limited regions which are the positional coordinate of thephase defect memorized as having the priority order in the step of S204and a periphery of the position.

<Steps S208 to S209>

If it is determined that the critical phase defect remains in the EUVLmask as a result of the inspection in the step of S207, a local portionto be adjusted of the above-described absorber pattern and an adjustmentdegree are calculated in order to reducing the influence of the phasedefect.

<Steps S212 to S213>

After finishing the above-described steps, if the portion to be adjustedexists in the absorber pattern, the above-described local absorberpattern is adjusted. It is accordingly checked whether the adjustmenthas been appropriately performed or not, by performing the inspectionusing the EUV light as the inspection light again, performing apractical exposure evaluation, or others. By the above-described step,steps of manufacturing the EUVL mask are finished.

<Steps S203 to S210>

On the other hand, in the step S203, if it is determined that the phasedefect does not exist in the mask blank, the absorber pattern is formedby the usual steps to manufacture the EUVL mask.

<Step S211>

Then, the conventional defect inspection for the absorber pattern isperformed. If the phase defect exists in the absorber pattern, theportion to be adjusted and an adjustment degree are separatelycalculated. Hereinafter, the process moves to the step of S212 followedby the above-described same steps, and steps of manufacturing the EUVLmask are finally finished.

As described above, by the method of manufacturing the mask according tothe second embodiment, the phase defect substantially existing in themanufactured EUVL mask can be significantly reduced, and besides, thedefect of the pattern projection image caused by the phase defectremaining in the multi-layered film of the EUVL mask can be recovered bythe adjustment of the absorber pattern. As a result, even if the phasedefect exists in the mask blank, the defect is substantially notdefective at the stage of the completion of the EUVL mask, so thatfrequency of a state that this is available as a non-defective productis increased. Therefore, a manufacture yield of the EUVL mask can besignificantly improved, and this can contribute to cost reduction of theEUVL mask.

In the foregoing, the invention made by the inventors has beenconcretely described based on the embodiments. However, it is needlessto say that the present invention is not limited to the foregoingembodiments and various modifications and alterations can be made withinthe scope of the present invention.

The present invention can be applied to a method of inspecting an EUVLmask using EUV light as inspection light, to an inspection device, andto a method of manufacturing the EUVL mask.

1. A method of inspecting a mask for reflecting EUV light comprising thesteps of: (a) irradiating the EUV light to the mask; (b) imaging the EUVlight which reflects from the mask onto a light-receiving plane of animage detector through a dark-field imaging optical system to form adark-field inspection image on the light-receiving plane; and (c)detecting a detection signal of a phase defect existing in the mask fromdetection signals obtained by the image detector, and the step of (a)further including the steps of: (a1) inputting information indicatingwhether an absorber pattern exists or not in an inspection region of themask; and (a2) changing illumination NA of the EUV light depending oneither a case that the absorber pattern exists or a case that theabsorber pattern does not exist.
 2. The method of inspecting the maskaccording to claim 1, wherein the dark-field imaging optical system is amagnifying optical system including a plurality of reflection mirrorsmade of a multi-layered film, and a pupil plane of the dark-fieldimaging optical system includes: a center shielding portion forshielding the EUV light arranged at center of the pupil plane; andlinear shielding portions for shielding the EUV light each arrangedalong an X axis and a Y axis orthogonal to the X axis and each having asmaller width than a diameter of the center shielding portion, in thecase that the absorber pattern does not exist, the phase defect existingin the mask is detected by irradiating the EUV light having illuminationNA within an inner NA but larger than the widths of the linear shieldingportions, and, in the case that the absorber pattern exists, the phasedefect existing in the mask is detected by irradiating the EUV lighthaving illumination NA as large as or smaller than the widths of thelinear shielding portions.
 3. A mask inspection device comprising: astage movable in an X direction and a Y direction orthogonal to the Xdirection, on which a mask having an absorber pattern is loaded; a lightsource of generating EUV light; an illumination optical system ofirradiating the EUV light to the mask; illumination aperture of changingillumination NA when the EUV light is irradiated to the mask; adark-field imaging optical system of collecting scattered light from themask and forming a dark-field inspection image; an image detector ofacquiring the dark-field inspection image as a pixel signal; and anaperture driving unit of adjusting the illumination aperture based oninformation of the absorber pattern.
 4. The mask inspection deviceaccording to claim 3, wherein a pupil plane of the dark-field imagingoptical system includes: a center shielding portion for shielding theEUV light arranged at center of the pupil plane; and linear shieldingportions for shielding the EUV light each arranged along an X axis and aY axis orthogonal to the X axis and each having a smaller width than adiameter of the center shielding portion.
 5. A method of manufacturing amask comprising the steps of: (a) preparing a mask blank obtained byforming a multi-layered film on a main plane of a substrate; (b)irradiating first EUV light to the mask blank to detect a phase defectof the mask blank; (c) memorizing a positional coordinate of the phasedefect of the mask blank detected in the step of (b) and providing apriority order, which indicates a degree of influence on patterntransfer, to the phase defect of the mask blank; (d) forming an absorberpattern on the multi-layered film to form a mask; and (e) detecting aphase defect of the mask by an inspection device using second EUV lightas inspection light, the step of (b) further including the steps of:(b1) irradiating the first EUV light having illumination NA within aninner NA to the mask blank; (b2) imaging the first EUV light reflectedfrom the mask blank onto a first light-receiving plane of a first imagedetector through a first dark-field imaging optical system, and forminga first dark-field inspection image on the first light-receiving plane;and (b3) detecting a detection signal of the phase defect of the maskblank from detection signals obtained by the first image detector, andthe step of (d) further including the step of: (d1) covering the phasedefect of the mask blank by the absorber pattern in a descending orderof the priority order.
 6. The method of manufacturing the mask accordingto claim 5, wherein a second dark-field imaging optical system of theinspection device used in the step of (e) includes: a center shieldingportion for shielding the second EUV light arranged at center of a pupilplane of the second dark-field imaging optical system; and linearshielding portions for shielding the second EUV light each arrangedalong an X axis and a Y axis orthogonal to the X axis and each having asmaller width than a diameter of the center shielding portion, and theillumination NA in the step of (b1) is within the inner NA but largerthan the widths of the linear shielding portions.
 7. The method ofmanufacturing the mask according to claim 5, wherein a second dark-fieldimaging optical system of the inspection device used in the step of (e)includes: a center shielding portion for shielding the second EUV lightarranged at center of a pupil plane of the second dark-field imagingoptical system; and linear shielding portions for shielding the secondEUV light each arranged along an X axis and a Y axis orthogonal to the Xaxis and each having a smaller width than a diameter of the centershielding portion, and the step of (e) further includes the steps of:(e1) irradiating the second EUV light having illumination NA as large asor smaller than the widths of the linear shielding portions to the mask;(e2) imaging the second EUV light reflected from the mask onto a secondlight-receiving plane of a second image detector through the seconddark-field imaging optical system, and forming a second dark-fieldinspection image on the second light-receiving plane; and (e3) detectinga detection signal of the phase defect of the mask from detectionsignals obtained by the second image detector.
 8. The method ofmanufacturing the mask according to claim 5, wherein the method furtherincludes: (f) detecting a phase defect not covered by the absorberpattern and remaining in the mask; (g) predicting influence of the phasedefect remaining in the mask on a transfer image; and (h) detecting aphase defect at which the influence can be reduced, and adjusting ashape of the absorber pattern adjacent to the phase defect at which theinfluence can be reduced.